Three-phase current generators

In electrical engineering, the term three-phase means a combined system of 3 alternating current circuits (for the production, distribution and use of electricity) having the same frequency and three equal alternating voltages, but out of phase with each other by 120 °.

Compared to a single-phase alternating current system, the cost of materials and electrical cables is halved for the same electrical power.

Advantages of a three-phase generator

The great importance of the three-phase system is due to three fundamental advantages:

• moment of rotation The presence of three out of phase signals allows to create a rotating magnetic field, at the basis of the operation of the electric motor. The motors used in household appliances, powered with one phase, are either not self-starting or require a capacitor to create a second power supply phase and be self-starting (in this case there is still a drop in efficiency).
• conductor optimization We can imagine the three generators of the three-phase system as three physically separate generators, each with its own two-wire line directed to the loads. In this case, the necessary threads would be six. Well, in the three-phase system these three generators are synchronized and out of phase by 120 °. If the three currents of the generators are also equal in modulus and out of phase by 120 ° (balanced system), the algebraic sum of the three currents circulating instant by instant in one of the two wires of each line is zero; it follows that if these three wires are connected together in a conductor, there is no current circulation on it, and then this wire can be eliminated. If, on the other hand, the system is not balanced, current will flow in this wire. The result is the ability to transport the same amount of energy using three wires instead of six, with great savings in copper or aluminum, especially on long power lines. In fact, observing a high-voltage power line, one notes the presence of three wires, called three wires (or multiple if the pylons carry more lines). In very high voltage lines (> 150 kV) each of the three phases is carried on multiple conductors, double or triple, in order to reduce the inductance and the corona effect, with the relative dispersive effects.
• less transport losses
  The third but no less important aspect of the three-phase system is the lower power dissipated along the electrical lines compared to a single-phase system (higher transmission efficiency). In fact, the energy of the three generators is transmitted with only three wires instead of six because there are no three current return lines for each phase. Consequently, the current path of each phase is halved and the line resistance is therefore halved; the loss of electric power for each phase (given by the formula P = R i ² ) along the power lines is therefore exactly half of the single-phase case.